The pathogenesis of idiopathic pulmonary fibrosis (IPF) is unknown. A central hypothesis is that the chronic accumulation of inflammatory and immune effector cells (alveolitis) produces the parenchymal cell injury that leads to fibrosis, with progressive irreversible loss of functioning alveolar-capillary units. Therefore, the major goals of this project are to improve our understanding of the immunopathogenesis of IPF and to develop and evaluate methods that can serially identify the presence and extent of disease activity in these patients.